South Korea president impeached

Anonymous declares war on Trump

Hacktivist group has called for hackers of the world to unite to disrupt the Trump Presidential campaign.

Citing an unnamed source, ABC News reported that the substance "was accompanied by a threatening note that said something to the effect of: Either Donald Trump drops out of the race or next time this will be real."

CBS News reported that the letter warned that "harm will come to the kids" if Donald Trump doesn't drop out.

Donald Trump and his son Eric (right) speak to supporters at his Mar-a-Lago Club in Palm Beach. Photo: AP

Preliminary tests showed that the substance was not hazardous, an official told The Post.

The Associated Press reported that the FBI is part of the investigation, and CBS reported that the Secret Service is also involved.

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The Trump campaign did not immediately respond to a request for comment. Nor did the Trump Organization, where Eric Trump - the billionaire businessman's third child - serves as executive vice president of development and acquisition.

Eric Trump has actively campaigned on behalf of his father, the Republican front-runner, and was with him Tuesday night in Palm Beach to celebrate primary wins in multiple states, including Florida, North Carolina and Illinois.

ABC reported that "the letter carried a Massachusetts postmark and was opened by Eric Trump's wife, Lara."

A law enforcement official told The Post that the envelope was opened "by a 33-year-old female," but would not release a name. Lara Trump is 33.

The threat comes days after white substances were delivered to Sen. Ted Cruz's campaign headquarters in Houston and to Sen. Marco Rubio's campaign headquarters in Washington. In both cases, the substances were non-toxic.

The powder sent to Rubio turned out to be laundry detergent, according to a spokesman for the senator's now-scuttled campaign.